A cold shower in the morning isn’t the most appealing way to start your day, but many do it because a cold water immersion has many purported health benefits, both physical and mental, including improved metabolism.
Some studies have found that cold water activates the sympathetic nervous system, the part of the nervous system that governs the fight-or-flight response (an automatic physiological reaction to an event that is perceived as dangerous, stressful or frightening). When this is activated, such as during a cold shower, you get an increase in the hormone noradrenaline. This is what most likely causes the observed increases in heart rate and blood pressure when people are immersed in cold water, and is linked to health improvements like endorphin release, improved circulation, and better metabolism.
However, a sudden gush of cold water can be dangerous for people with pre-existing heart disease and could precipitate a heart attack or heart-rhythm irregularities, so before trying this out please check with your doctor first.
Click here to read more about cold water and health:
The effect of cold showering on health and work: a randomized controlled trial